Wireless power transfer for implanted medical devices is a known and well-studied subject. The traditional approach is TET (transcutaneous energy transfer), in which the energy source is directed toward the energy harvesting device with the goal to minimize RF exposure of the patient. In one commercial embodiment, the receiver coils are located under the patient's skin and the transmitter above the skin. Such TET systems are very sensitive to misalignment and movement of the implanted coil. Additionally, the coil implanted in a separate surgical procedure. Another shortcoming of the current TET solution is that the electromagnetic field density is so high that it can cause heating of the skin and even burns. That is, when the receiver is receiving energy, regular resistance losses within the coil can cause heating to the same volume of tissue receiving the electromagnetic radiation and add heating to it. When the transmitter attached to the receiver is transmitting energy, regular resistance losses within the transmitter coil can cause heating that adds to the receiver regular resistance losses heating and to the receiving electromagnetic radiation heating. The accumulated heat can become a complex issue. TET systems have also suffered setbacks due to complexity and lack of efficiency.
Because of the heating issues, there is no TET system commercially available for use with a ventricular assist device (VAD). In current VAD systems, the power needed for the pump is delivered via an external power pack by a transcutaneous power line. The exit site of the drive line from the abdomen provides a portal of entry for pathogens, making VAD recipients highly vulnerable to device-related infections. However infectious complications are not limited to VAD systems, as infections are common in many medical devices that use transcutaneous power line.
There have been many attempts to develop a superior wireless power transfer system for use with implanted medical devices. Some known wireless power transfer approaches are described in U.S. Pat. Nos. 6,772,011, 7,741,734, 7,825,543, 7,613,497, 7,825,776, and 7,956,725 and in U.S. Patent Application Publication Nos. 2007-0132587, 2007-0182578, 2008-0041930, 2008-0238680, 2009-0243813, 2010-0045114, 2010-0052811, 2010-0081379, and 2010-0187913, all of which are incorporated herein by reference in their entireties.